Dirac's hole theory versus quantum field theory

Dirac's hole theory and quantum field theory are usually considered equivalent to each other. For models of a certain type, however, the equivalence may not hold as we discuss in this Letter. This problem is closely related to the validity of the Pauli principle in intermediate states of perturbation theory.Comment: No figure

Scaling relations for diversity of languages

The distribution of living languages is investigated and scaling relations are found for the diversity of languages as a function of the country area and population. These results are compared with data from Ecology and from computer simulations of fragmentation dynamics where similar scalings appear. The language size distribution is also studied and shown to display two scaling regions: (i) one for the largest (in population) languages and (ii) another one for intermediate-size languages. It is then argued that these two classes of languages may have distinct growth dynamics, being distributed on the sets of different fractal dimensions.Comment: 10 pages, 4 figure

Emerging from Crisis: the Mediterranean Neighborhood

So far, developing countries like the countries of the Mediterranean region seem to have been far less affected by the and started to recover earlier crisis than industrial countries. However, the region faces several problems like high unemployment and high inflation in the long term due to higher government consumption.Mediterranean countries, economic crisis, economic recovery